Skiving cutter

ABSTRACT

A skiving cutter includes a cutting edge portion in which a tooth trace extends in a direction inclined with respect to an axis of a base. The cutting edge portion is segmented into a plurality of segmented cutting edges by cutting edge grooves extending in a direction intersecting the tooth trace. A helix angle is different according to positions of the plurality of segmented cutting edges.

This application is a Continuation of U.S. application Ser. No.15/769,504, filed on Apr. 19, 2018, which is the National Phase under 35U.S.C. § 371 of International Application No. PCT/JP2017/025958, filedon Jul. 18, 2017, which claims priority under 35 U.S.C. § 119(a) toApplication No. 2016-208537, filed in Japan on Oct. 25, 2016, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present invention relates to a skiving cutter for manufacturinginternal gears by skiving-processing internal gear materials.

BACKGROUND ART

For example, a skiving cutter disclosed in the following PatentLiterature 1 includes a base having a barrel shape or a truncated coneshape, and a plurality of cutting edge portions protruding from an outercircumferential surface of the base. Here, the truncated cone shape is ashape of a portion in which a cone is cut away at a plane parallel to abottom surface and a side including the apex of the cone is removed. Theplurality of cutting edge portions are separated from each other in acircumferential direction with respect to a central axis of the base. Atooth trace of each cutting edge portion extends in a direction inclinedwith respect to the central axis. In addition, a cutting edge portion isdivided into a plurality of segmented cutting edges by cutting edgegrooves extending in a direction intersecting the tooth trace.

CITATION LIST Patent Literature [Patent Literature 1]

Japanese Patent No. 5864035

SUMMARY OF INVENTION Technical Problem

A manufacturer of internal gears requires precision processing ofinternal gears into target shapes and to prolong a service life of thecutter used for manufacturing internal gears.

Therefore, it is an object of the present invention to provide a skivingcutter capable of precisely forming an internal gear into a target shapeand achieving a long service life for the skiving cutter.

Solution to Problem

A skiving cutter as a first aspect according to the invention forachieving the above-described object includes a base having a circularcross-sectional shape perpendicular to an axis, and a plurality ofcutting edge portions protruding from an outer circumferential surfaceof the base, formed at intervals in a circumferential direction withrespect to the axis, and having a tooth trace extending in a directioninclined with respect to the axis, in which each of the cutting edgeportions is segmented into a plurality of segmented cutting edges bycutting edge grooves extending in a direction intersecting the toothtrace, each of the segmented cutting edges includes an outercircumferential cutting edge which is an edge farthest away from thebase among portions forming the segmented cutting edge, one of theplurality of segmented cutting edges constituting the cutting edgeportion forms a reference cutting edge, and the reference cutting edgehas the largest axis-cutting edge distance which is a distance from theaxis to the outer circumferential cutting edge and the remaining one ormore segmented cutting edges have gradually smaller axis-cutting edgedistances as a distance from the reference cutting edge to each of theremaining segmented cutting edges increases, and a helix angle which isan angle of the tooth trace with respect to the axis is differentaccording to a position in the axial direction of the plurality ofsegmented cutting edges constituting the cutting edge portion.

Here, an internal gear in which the tooth trace is inclined with respectto a workpiece center axis and a helix angle of the tooth trace isconstant at any position in a direction in which the workpiece centeraxis extends is assumed to be processed by the method of the skivingprocessing. In the skiving cutter, the reference cutting edge has thelargest axis-cutting edge distance and the remaining one or moresegmented cutting edges among the plurality of segmented cutting edgesconstituting the cutting edge portion have gradually smalleraxis-cutting edge distances as a distance from the reference cuttingedge to each of the remaining segmented cutting edges increases. Thus,in the skiving cutter, when a cutting edge groove of a workpiece isbeing cut by one cutting edge portion among the plurality of cuttingedge portions, it is possible to prevent another cutting edge portionfrom cutting a region that is not supposed to be cut in the workpiece.

Also, in the skiving cutter, the helix angle which is an angle of thetooth trace with respect to the axis is different according to aposition in the axial direction of the plurality of segmented cuttingedges constituting the cutting edge portion. Therefore, in the skivingcutter, all the segmented cutting edges constituting the cutting edgeportion can be positioned at accurate positions with respect to thetooth groove of the workpiece. Therefore, in the skiving cutter, it ispossible to enhance processing accuracy for the workpiece. In addition,in the skiving cutter, since all the segmented cutting edgesconstituting the cutting edge portion can be positioned at accuratepositions with respect to tooth grooves of the workpiece, a load appliedto each of the segmented cutting edges constituting the cutting edgeportion can be reduced and a service life of the skiving cutter can beprolonged.

Here, in the skiving cutter, helix angles of one or more segmentedcutting edges excluding the reference cutting edge among the pluralityof segmented cutting edges constituting the cutting edge portion mayincrease in variation amount with respect to the helix angle of thereference cutting edge as a distance from the reference cutting edge toeach of the segmented cutting edges increases.

In the skiving cutter, all the segmented cutting edges constituting thecutting edge portion can be positioned at more accurate positions withrespect to tooth grooves of the workpiece.

In addition, in any of the skiving cutters described above, helix anglesof one or more segmented cutting edges excluding the reference cuttingedge among the plurality of segmented cutting edges constituting thecutting edge portion may increase as a distance increases from thereference cutting edge to each of the segmented cutting edges.

In the skiving cutter, all the segmented cutting edges constituting thecutting edge portion can be positioned at more accurate positions withrespect to tooth grooves of the workpiece.

In any of the skiving cutters described above, cutting edge heights ofthe plurality of segmented cutting edges constituting the cutting edgeportion may be formed such that the cutting edge height at the referencecutting edge is the highest, and the cutting edge height at onesegmented cutting edge which is more distant from the reference cuttingedge between two segmented cutting edges adjacent to each other in atooth trace direction in which the tooth trace extends is equal to orless than the cutting edge height of the other segmented cutting edge.

In the skiving cutter, an amount of wear on the plurality of segmentedcutting edges constituting the cutting edge can be made uniform, and aservice life of the skiving cutter can be prolonged.

In any of the skiving cutters described above, cutting edge widths ofthe plurality of segmented cutting edges constituting the cutting edgeportion may be formed such that the cutting edge width at the referencecutting edge is the largest, and the cutting edge width at one segmentedcutting edge which is more distant from the reference cutting edgebetween the two segmented cutting edges adjacent to each other in thetooth trace direction in which the tooth trace extends is equal to orless than the cutting edge width of the other segmented cutting edge.

In the skiving cutter, an amount of wear on the plurality of segmentedcutting edges constituting the cutting edge portion can be made uniform,and a service life of the skiving cutter can be prolonged.

In any of the skiving cutters described above, the segmented cuttingedges may include a cutting face extending from the outercircumferential cutting edge toward the base, a peripheral relief faceextending from the outer circumferential cutting edge in a directionalong the tooth trace, and a back face extending from an end opposite tothe outer circumferential cutting edge on the peripheral relief facetoward the base, and a rake angle which is an angle of the cutting facewith respect to a virtual plane perpendicular to the tooth trace may be0° or more and 20° or less.

In the skiving cutter, in contrast to a case in which the rake angle isless than 0°, the cutting load decreases and a wear amount of thecutting edge can be reduced. In addition, in the skiving cutter, incontrast to a case in which the rake angle exceeds 20°, strength of thecutting edge can be enhanced and a risk of causing chipping or the likecan be reduced.

Further, in the skiving cutter having the back face, a back face anglewhich is an angle of the back face with respect to a virtual planeperpendicular to the tooth trace may be 10° or more and 50° or less.

In the skiving cutter, in contrast to a case in which the back faceangle is less than 10°, swarf discharge can be smoothly performed. Also,in the skiving cutter, in contrast to a case in which the back faceangle is larger than 50°, when it is assumed that a length of theperipheral relief face in a direction in which the tooth trace L extendsis made constant, it is possible to reduce a length of the segmentedcutting edge in a direction in which the tooth trace extends. When it isassumed that a length of the segmented cutting edge in a direction inwhich the tooth trace extends is made constant, it is possible toprevent a length of the peripheral relief face in a direction in whichthe tooth trace extends from becoming unnecessarily short.

In the skiving cutter having the peripheral relief face, a peripheralrelief angle which is an angle of the peripheral relief face withrespect to the tooth trace may be more than 0° and 12° or less.

In the skiving cutter, in contrast to a case in which the peripheralrelief angle is equal to or less than 0°, rubbing of a tooth bottomportion of an internal gear with the peripheral relief face can beprevented, deterioration of surface characteristics in the tooth bottomportion of the internal gear can be reduced, and abrasion of theperipheral relief face can be reduced. In addition, in the skivingcutter, in contrast to a case in which the peripheral relief angleexceeds 12°, a cutter having an increased effective tooth width can beeasily manufactured, and a service life of the cutter can be easilyprolonged.

In any of the skiving cutters described above, the outer circumferentialcutting edge of the segmented cutting edge having a helix angle of 10°or less may be in a virtual plane perpendicular to the axis.

In the skiving cutter, all of the outer circumferential cutting edges ofthe plurality of segmented cutting edges having the same position in theaxial direction as each other extend in one virtual plane perpendicularto the axis. Therefore, in the skiving cutter, each of the outercircumferential cutting edges of the plurality of segmented cuttingedges having the same position in the axial direction as each other anda cutting face which is continuous with the outer circumferentialcutting edge can be processed together with mutually adjacent segmentedcutting edges in the circumferential direction.

In any of the skiving cutters described above, the outer circumferentialcutting edge of the segmented cutting edge having the helix angle αlarger than 10° may be in a virtual plane perpendicular to the toothtrace.

In the skiving cutter, a direction in which the tooth trace extends is acutting direction. Therefore, when the outer circumferential cuttingedge extends in the virtual plane perpendicular to the tooth trace,cutting loads at portions on both sides of the outer circumferentialcutting edge are made equal and an amount of wear at each position onthe outer circumferential cutting edge can be made uniform.

In any of the skiving cutters described above, the skiving cutter mayinclude a plurality of cutter pieces arranged in the axial direction, inwhich each of the cutter pieces has a segmented cutting edge row whichis a collection of a plurality of segmented cutting edges having thesame position in the axial direction as each other and arranged in thecircumferential direction among the segmented cutting edges constitutingeach of the plurality of cutting edge portions, and a segmented baseformed as a portion of the base and including the segmented cutting edgerow formed on an outer circumference thereof, the segmented bases areseparable from each other, and the skiving cutter may further include apositioning member which determines relative positions in thecircumferential direction of the segmented cutting edges between theplurality of cutter pieces.

The skiving cutter includes a plurality of segmented bases which areseparable from each other, and furthermore, among the plurality ofsegmented cutting edges constituting one cutting edge portion, only onesegmented cutting edge is formed on one segmented base. Therefore, amongthe plurality of segmented cutting edges constituting one cutting edgeportion, it is possible to process one segmented cutting edge withoutinterfering with the other segmented cutting edges constituting thecutting edge portion.

Advantageous Effects of Invention

According to the skiving cutter of one aspect of the present invention,an internal gear can be precisely formed into a target shape and aservice life of the skiving cutter can be prolonged.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a skiving machine in a first embodiment.

FIG. 2 is a perspective view of a skiving cutter in the firstembodiment.

FIG. 3 is a cross-sectional view taken along line in FIG. 2.

FIG. 4 is a perspective view of a segmented cutting edge in the firstembodiment.

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4.

FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4.

FIG. 7 is an explanatory view for describing sizes of a plurality ofsegmented cutting edges constituting a cutting edge portion in the firstembodiment.

FIG. 8 is an explanatory view illustrating helix angles andcircumferential positions of the plurality of segmented cutting edgesconstituting the cutting edge portion in the first embodiment.

FIG. 9 is a graph showing an amount of variation in helix angle of theplurality of segmented cutting edges constituting the cutting edgeportion in the first embodiment.

FIG. 10 is a perspective view of a skiving cutter and a workpiece whichare in a processing state in the first embodiment.

FIG. 11 is a side view of a skiving cutter which is in a processingstate in the first embodiment.

FIG. 12 is a side view of a skiving cutter in a second embodiment.

FIG. 13 is a side view of a skiving cutter in a third embodiment.

FIG. 14 is a perspective view of a skiving cutter in the thirdembodiment.

FIG. 15 is a cross-sectional view taken along line XV-XV in FIG. 14.

FIG. 16 is a side view of a skiving cutter in a fourth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, various embodiments of a skiving cutter according to thepresent invention will be described with reference to the drawings.

First Embodiment

A first embodiment of a skiving cutter will be described with referenceto FIGS. 1 to 11.

First, a skiving machine on which a skiving cutter is mounted will bedescribed.

As illustrated in FIG. 1, a skiving machine includes a bed 1, a column2, a saddle 3, a head 4, a slider 5, a main spindle unit 6, and a rotarytable 7.

The column 2 extends in a vertical direction. Here, the verticaldirection is referred to as a Z direction, a direction perpendicular tothe Z direction is referred to as a Y direction, and a directionperpendicular to the Z direction and the Y direction is referred to asan X direction. This column 2 is attached to the bed 1 to be movable inthe X direction. The saddle 3 is attached to the column 2 to be movablein the Z direction. The head 4 is attached to the saddle 3 to berotatable around a head center axis Ah extending in the X direction. Theslider 5 is attached to the head 4 to be movable in a directionperpendicular to the head center axis Ah. The main spindle unit 6 isfixed to the slider 5. The main spindle unit 6 holds a skiving cutter100 via a cutter arbor 10 and rotates the skiving cutter 100 around amain spindle rotation axis Am. A cutter center axis Ac, which is arotational center axis of the skiving cutter 100, is positioned on anextension line of the main spindle rotation axis Am of the main spindleunit 6 in a state in which the skiving cutter 100 is held by the mainspindle unit 6.

The rotary table 7 is disposed on the bed 1 at a position away from thecolumn 2 in the X direction. This rotary table 7 is provided on the bed1 to be rotatable around a table rotation axis At extending in the Zdirection. On this rotary table 7, a workpiece holder 19 for holding acylindrical workpiece W which is an internal gear material is attached.

As illustrated in FIGS. 2 and 3, the skiving cutter 100 includes abarrel-shaped base 110 centered on the cutter center axis Ac and aplurality of cutting edge portions 120 protruding from an outercircumferential surface of the base 110. In the following description, adirection in which the cutter center axis Ac extends is referred to asan axial direction Da, and a circumferential direction with respect tothe cutter center axis Ac is simply referred to as a circumferentialdirection Dc. In addition, one side in the axial direction Da isreferred to as a distal end side Daa, and the other side is referred toas an attachment side Dab.

As described above, the base 110 has a barrel shape centered on thecutter center axis Ac. Therefore, at any position in the axial directionDa, the base 110 has a circular cross-sectional shape perpendicular tothe cutter center axis Ac. The base 110 has a maximum outer diameter ata central position in the axial direction Da and an outer diametergradually decreases from the central position toward the distal end sideDaa and the attachment side Dab. An attachment hole 112 penetrating inthe axial direction Da is formed in the base 110. The attachment hole112 has a columnar shape centering on the cutter center axis Ac. Thebase 110 further has a key groove 113 recessed to a radial outer sidewith respect to the cutter center axis Ac from an inner circumferentialsurface of the attachment hole 112. The key groove 113 extends in theaxial direction Da from an end face on the attachment side Dab to an endface on the distal end side Daa of the base 110.

The cutter arbor 10 includes a cutter attachment portion 12 that can beinserted into the attachment hole 112 of the skiving cutter 100 and aheld portion 15 that is held by the main spindle unit 6. Both of thecutter attachment portion 12 and the held portion 15 have a columnarshape with an arbor center axis Aa as the center. The arbor center axisAa coincides with the cutter center axis Ac in a state in which thecutter attachment portion 12 is inserted in the attachment hole 112 ofthe skiving cutter 100. Therefore, hereinafter, for convenience, adirection in which the arbor center axis Aa extends is also referred toas the axial direction Da which is a direction in which the cuttercenter axis Ac extends, and one side in the direction in which the arborcenter axis Aa extends is referred to as the distal end side Daa and theother side is referred to as the attachment side Dab.

An outer diameter of the held portion 15 is larger than an outerdiameter of the cutter attachment portion 12. The cutter attachmentportion 12 is provided on the distal end side Daa of the held portion15. A key groove 13 recessed to a radial inner side with respect to thearbor center axis Aa from an outer circumferential surface of the cutterattachment portion 12 is formed in the cutter attachment portion 12. Thekey groove 13 extends in the axial direction Da. A male screw 14 isformed at a portion of the cutter attachment portion 12 on the distalend side Daa.

When the skiving cutter 100 is attached to the cutter arbor 10, first,the cutter attachment portion 12 of the cutter arbor 10 is inserted intothe attachment hole 112 of the skiving cutter 100. Next, a key 17 isinserted into a key space formed by the key groove 113 of the skivingcutter 100 and the key groove 13 of the cutter arbor 10. Then, a fixingnut 18 is screwed into the male screw 14 of the cutter arbor 10.Thereby, attachment of the skiving cutter 100 to the cutter arbor 10 iscompleted.

The plurality of cutting edge portions 120 are separated from each otherin the circumferential direction Dc. A tooth trace L of each of thecutting edge portions 120 extends in a direction inclined with respectto the cutter center axis Ac. Also, the cutting edge portion 120 isdivided into a plurality of segmented cutting edges 122 by cutting edgegrooves 121 extending in a direction intersecting the tooth trace L. Inthe present embodiment, one cutting edge portion 120 has four or fivesegmented cutting edges 122. In FIG. 3, for convenience, the pluralityof segmented cutting edges 122 constituting one cutting edge portion 120are drawn in the axial direction Da in a virtual plane including thecutter center axis Ac.

As illustrated in FIGS. 4 to 6, the segmented cutting edges 122 includean outer circumferential cutting edge 123, a pair of side cutting edges124, a cutting face 125, an peripheral relief face 126, a back face 127,and a pair of side flank faces 128. Each of the cutting face 125, thepair of side flank faces 128, and the back face 127 extends from theouter circumferential surface of the base 110 toward the radial outerside with respect to the cutter center axis Ac. The cutting face 125 isdirected toward the distal end side Daa in a direction in which thetooth trace L extends. The pair of side flank faces 128 are directed ina direction having a directional component perpendicular to the toothtrace L. The pair of side flank faces 128 are in a back-to-backrelationship with each other. The back face 127 is positioned on theattachment side Dab in a direction in which the tooth trace L extendswith respect to the cutting face 125 and is directed to the attachmentside Dab in a direction in which the tooth trace L extends. The backface 127 is in a back-to-back relationship with the cutting face 125.The peripheral relief face 126 extends in a direction along the toothtrace L from an edge of the radial outer side of the cutting face 125 toan edge of the radial outer side of the back face 127. The outercircumferential cutting edge 123 is formed by an edge which is a cornerof the cutting face 125 and the peripheral relief face 126. Therefore,the cutting face 125 extends from the outer circumferential cutting edge123 toward a side approaching the base 110. Also, the back face 127extends from an end opposite to the outer circumferential cutting edge123 on the peripheral relief face 126 to the base 110 side. The outercircumferential cutting edge 123 is farthest away from the base 110among constituent portions of the segmented cutting edge 122. The sidecutting edge 124 is formed by an edge which is a corner of the cuttingface 125 and the side flank face 128.

As illustrated in FIG. 5, a rake angle θ1 which is an angle of thecutting face 125 with respect to a virtual plane Pa perpendicular to thetooth trace L is 0° or more and 20° or less. When the rake angle θ1 isless than 0°, there is a likelihood that the cutting load increases,surface characteristics of the worked surface deteriorate, and an amountof wear increases. Also, when the rake angle θ1 exceeds 20°, there is alikelihood that a strength of the cutting edge deteriorates, therebycausing occurrence of chipping or the like. Therefore, the rake angle θ1is preferably within the angle range described above.

An peripheral relief angle θ2, which is an angle of the peripheralrelief face 126 with respect to the tooth trace L, is larger than 0° and12° or less. When the peripheral relief angle θ2 is equal to or lessthan 0°, a tooth bottom portion of an internal gear is rubbed by theperipheral relief face 126, surface properties of the tooth bottomportion of the internal gear deteriorate, and an amount of wear on theperipheral relief face 126 increases. Also, when the peripheral reliefangle θ2 exceeds 12°, a cutter having an increased effective tooth widthcannot be easily manufactured, and a service life of the cutter cannotbe easily prolonged. Therefore, the peripheral relief angle θ2 ispreferably within the angle range described above. Further, it isparticularly preferable that the peripheral relief angle θ2 be 5° ormore. When the peripheral relief angle θ2 is 5° or more, it is possibleto reliably avoid rubbing of the peripheral relief face 126 due tospring back caused by elastic deformation of the segmented cutting edges122 at the time of cutting.

A back face angle θ3, which is an angle of the back face 127 withrespect to the virtual plane Pa perpendicular to the tooth trace L, is10° or more and 50° or less. When the back face angle θ3 is less than10°, swarf discharge from the outer circumferential cutting edge 123 ofa segmented cutting edge 122 positioned on the attachment side Dab fromthe segmented cutting edge 122 may not be performed smoothly. Also, ifthe back face angle θ3 is larger than 50°, when it is assumed that alength of the peripheral relief face 126 in a direction in which thetooth trace L extends is made constant, a length of the segmentedcutting edges 122 in a direction in which the tooth trace L extendsbecomes unnecessarily long. In addition, if the back face angle θ3 islarger than 50°, when it is assumed that the length of the segmentedcutting edge 122 in the direction in which the tooth trace L extends ismade constant, a length of the peripheral relief face 126 in thedirection in which the tooth trace L extends becomes unnecessarilyshort. Therefore, the back face angle θ3 is preferably within the anglerange described above.

As illustrated in FIG. 6, a side relief angle θ4, which is an angle ofthe side flank face 128 with respect to the tooth trace L, is largerthan 0° and 5° or less. When the side relief angle θ4 is 0° or less,there is a likelihood that a cutting load increases, surface propertiesof the worked surface deteriorate, and an amount of wear increases. Whenthe side relief angle θ4 exceeds 20°, there is a likelihood thatstrength of the cutting edge deteriorates, thereby causing occurrence ofchipping or the like. Therefore, the side relief angle θ4 is preferablywithin the angle range described above. Further, it is particularlypreferable that the side relief angle θ4 be 2° or more.

As illustrated in FIG. 4, between a pair of groove side faces formingthe cutting edge groove 121, one side face forms the back face 127 of asegmented cutting edge 122, and the other side face forms the cuttingface 125 of a segmented cutting edge 122.

Here, as illustrated in FIG. 3, among the plurality of cutting edges 122constituting the cutting edge portion 120, the segmented cutting edge122 formed on the base 110 at a central portion in the axial directionDa is referred to as a finishing cutting edge (reference cutting edge)122 a, and the remaining segmented cutting edges 122 are referred to ascoarse cutting edges 122 b and 122 c. Also, a distance from the cuttercenter axis Ac to the outer circumferential cutting edge 123 is referredto as an axis-cutting edge distance D. Among the axis-cutting edgedistances D of the plurality of segmented cutting edges 122 constitutingthe cutting edge portion 120, an axis-cutting edge distance D0 of thefinishing cutting edge 122 a is the largest. As a distance from thefinishing cutting edge 122 a increases, the axis-cutting edge distance Dof the plurality of coarse cutting edges 122 b and 122 c graduallydecreases. In other words, an axis-cutting edge distance D1 of a firstcoarse cutting edge 122 b adjacent to the finishing cutting edge 122 ain a direction in which the tooth trace L extends is the next largestafter the axis-cutting edge distance D0 of the finishing cutting edge122 a. An axis-cutting edge distance D2 of a second coarse cutting edge122 c adjacent to the first coarse cutting edge 122 b on a side oppositeto the finishing cutting edge 122 a in a direction in which the toothtrace L extends is the next largest after the axis-cutting edge distanceD1 of the first coarse cutting edge 122 b. That is, the axis-cuttingedge distance D decreases in the order of the finishing cutting edge 122a, the first coarse cutting edge 122 b, and the second coarse cuttingedge 122 c.

As illustrated in FIG. 7, a cutting edge height h0 of the finishingcutting edge 122 a is the largest among cutting edge heights h of theplurality of segmented cutting edges 122 constituting the cutting edgeportion 120. Among the plurality of segmented cutting edges 122constituting the cutting edge portion 120, between two segmented cuttingedges 122 adjacent to each other in a tooth trace direction in which thetooth trace L extends, a cutting edge height h of one of the segmentedcutting edges 122 which is more distant from the finishing cutting edge122 a is equal to or less than a cutting edge height h of the othersegmented cutting edge 122. In other words, a cutting edge height h1 ofthe coarse cutting edge 122 b is equal to or less than the cutting edgeheight h0 of the finishing cutting edge 122 a, and a cutting edge heighth2 of the coarse cutting edge 122 c is equal to or less than the cuttingedge height h1 of the coarse cutting edge 122 b. Therefore, in thepresent embodiment, the segmented cutting edge 122 on the distal endside Daa has the smallest cutting edge height h, and the cutting edgeheight increases as a position of the segmented cutting edge 122 becomescloser to the attachment side Dab until reaching the finishing cuttingedge 122 a.

In addition, among the cutting edge widths w of the plurality ofsegmented cutting edges 122 constituting the cutting edge portion 120, acutting edge width w0 of the finishing cutting edge 122 a is thelargest. Among the plurality of segmented cutting edges 122 constitutingthe cutting edge portion 120, between two segmented cutting edges 122adjacent to each other in the tooth trace direction, a cutting edgewidth w of one of the segmented cutting edges 122 which is more distantfrom the finishing cutting edge 122 a is equal to or less than a cuttingedge width w of the other segmented cutting edge 122. That is, a cuttingedge width w1 of the coarse cutting edge 122 b is equal to or less thanthe cutting edge width w0 of the finishing cutting edge 122 a, and acutting edge width w2 of the coarse cutting edges 122 c is equal to orless than the cutting edge width w2 of the coarse cutting edges 122 b.Therefore, in the present embodiment, the segmented cutting edge 122 onthe distal end side Daa has the narrowest cutting edge width, and thecutting edge width increases as a position of the segmented cutting edge122 becomes closer to the attachment side Dab until reaching thefinishing cutting edge 122 a.

As illustrated in FIG. 8, a helix angle α, which is an angle of thetooth trace L with respect to the cutter center axis Ac, is differentaccording to a position of the tooth trace L in the axial direction Da.Therefore, the helix angle α for each of the plurality of segmentedcutting edges 122 constituting the cutting edge portion 120 is differentaccording to a position of each segmented cutting edge 122 in the axialdirection Da. In other words, the helix angle α for each of theplurality of coarse cutting edges 122 b and 122 c is different accordingto a distance from the finishing cutting edge 122 a to each of thecoarse cutting edges 122 b and 122 c. In addition, due to therelationship in which the helix angle α of the tooth trace L isdifferent according to a position in the axial direction Da of the toothtrace L, positions of the plurality of segmented cutting edges 122 in acircumferential direction Dc are different in contrast to a case inwhich the helix angle α is constant at each position in the axialdirection Da. Further, FIG. 8 illustrates a state in which an outercircumferential surface of the base 110 is deployed on a plane.

As shown in FIG. 9, variation amounts Δ1 and Δ2 of the helix angle α ofeach of the coarse cutting edges 122 b and 122 c with respect to a helixangle α0 of the finishing cutting edge 122 a increase as a distance fromthe finishing cutting edge 122 a increases. That is, a variation amountΔ2 of the helix angle α of the second coarse cutting edge 122 c islarger than a variation amount Δ1 of the helix angle α of the firstcoarse cutting edge 122 b.

In addition, as illustrated in FIG. 8, the helix angles α1 and α2 of theplurality of segmented cutting edges 122 b and 122 c excluding thefinishing cutting edge 122 a among the plurality of segmented cuttingedges 122 constituting the cutting edge portion 120 increase as adistance from the finishing cutting edge 122 a to the segmented cuttingedges 122 b and 122 c increases. Further, in FIG. 8, α0 is the helixangle of the finishing cutting edge 122 a, α1 is the helix angle of thefirst coarse cutting edge 122 b, and α2 is the helix angle of the secondcoarse cutting edge 122 c.

When manufacturing an internal gear, as illustrated in FIG. 1, acylindrical workpiece W, which is an internal gear material, is held bythe workpiece holder 19 on the rotary table 7. At this time, the tablerotation axis At of the rotary table 7 and a workpiece center axis Awwhich is a central axis of the cylindrical workpiece W coincide witheach other. Further, the skiving cutter 100 described above is mountedon the main spindle unit 6 of the skiving machine. Next, the head 4rotates around the head center axis Ah with respect to the saddle 3, andthe main spindle rotation axis Am of the main spindle unit 6 is inclinedwith respect to the workpiece center axis Aw. Further, a sequentialorder of executing the above-described processes is not limited to thesequential order described above. As a result, as illustrated in FIGS.10 and 11, the cutter center axis Ac is inclined with respect to theworkpiece center axis Aw. In this state, the workpiece W rotates aroundthe workpiece center axis Aw and the skiving cutter 100 reciprocates inthe Z direction while rotating around the cutter center axis Ac. Asdescribed above, a method of skiving processing is a method ofprocessing the workpiece W in a state in which the cutter center axis Acis inclined with respect to the workpiece center axis Aw.

In this method of the skiving process, as illustrated in FIGS. 10 and11, among the plurality of segmented cutting edges 122 constituting thecutting edge portion 120, a segmented cutting edge 122 on the attachmentside Dab with respect to the finishing cutting edge 122 a does not comeinto contact with the workpiece W. That is, among the plurality ofsegmented cutting edges 122 constituting the cutting edge portion 120,the segmented cutting edge 122 on the attachment side Dab with respectto the finishing cutting edge 122 a does not contribute to the skivingprocessing.

Among the plurality of segmented cutting edges 122 constituting thecutting edge portion 120, the segmented cutting edge 122 c furthesttoward the distal end side Daa comes into contact with the workpiece Wfirst, the segmented cutting edge 122 b next after the segmented cuttingedge 122 c from the attachment side Dab subsequently comes into contactwith the workpiece W, and the segmented cutting edge 122 a which isfurthest toward the attachment side Dab subsequently comes into contactwith the workpiece W. That is, in the present embodiment, the secondcoarse cutting edge 122 c comes into contact with the workpiece W first,then the first coarse cutting edge 122 b subsequently comes into contactwith the workpiece W, and the finishing cutting edge 122 a comes intocontact with the workpiece W finally.

When it is assumed that the plurality of segmented cutting edges 122constituting the cutting edge portion 120 have the same cutting edgeheight and the same cutting edge width, a cutting load applied to thesegmented cutting edge 122 c furthest toward the distal end side Daa issignificantly higher than the cutting load applied to the remainingsegmented cutting edges 122, and an amount of wear on the segmentedcutting edge 122 c furthest toward the distal end side Daa is largerthan an amount of wear on the remaining segmented cutting edges 122. Onthe other hand, in the present embodiment, since the cutting edge heightof the segmented cutting edges 122 increases as a position thereofbecomes closer to the attachment side Dab from the distal end side Daaand the cutting edge width of the segmented cutting edges 122 increasesas a position thereof becomes closer to the attachment side Dab from thedistal end side Daa, an amount of wear on the plurality of segmentedcutting edges 122 can be made uniform, and the service life of theskiving cutter 100 can be prolonged.

Here, as illustrated in FIG. 10, an internal gear in which a tooth traceLw is inclined with respect to the workpiece center axis Aw and a helixangle of the tooth trace Lw is constant at any position in a directionin which the workpiece center axis Aw extends is assumed to be processedby the method of the skiving processing. Further, it is assumed that theaxis-cutting edge distances D of the plurality of segmented cuttingedges 122 constituting the cutting edge portion 120 of the skivingcutter 100 are constant. In other words, an outer shape of the skivingcutter 100 is cylindrical. In this case, depending on an inclinationangle of the cutter center axis Ac with respect to the workpiece centeraxis Aw, when a cutting edge groove of the workpiece W is being cut byone cutting edge portion 120 among the plurality of cutting edgeportions 120, another cutting edge portion 120 may cut a region that isnot supposed to be cut in the workpiece W in some cases. In the presentembodiment, the axis-cutting edge distance D of the finishing cuttingedge 122 a is the largest in the plurality of cutting edges 122constituting the cutting edge portion 120, and the axis-cutting edgedistance D of the coarse cutting edges 122 b and 122 c graduallydecreases as the distance from the finishing cutting edge 122 a to eachof the coarse cutting edges 122 b and 122 c increases. Therefore, in theskiving cutter 100 of the present embodiment, when a tooth groove of theworkpiece W is being cut by one cutting edge portion 120 among theplurality of cutting edge portions 120, it is possible to preventanother cutting edge portion 120 from cutting a region in the workpieceW that is not supposed to be cut.

The inventor found that a processing accuracy for each tooth of theinternal gear does not meet expected processing accuracy when theworkpiece W is processed by the method of the skiving processing withthe skiving cutter 100 in which the plurality of segmented cutting edges122 are set such that the axis-cutting edge distance D is the largest atthe finishing cutting edge 122 a and the axis-cutting edge distance Dgradually decreases as the distance from the finishing cutting edge 122a to each of the coarse cutting edges 122 b and 122 c increases.Therefore, the inventor simulated processing of the workpiece W usingthe skiving cutter 100 having a constant helix angle α at each of theplurality of segmented cutting edges 122 constituting the cutting edgeportion 120 on a computer. The result was that when one cutting edgeportion 120 processed one tooth groove in the workpiece W, asillustrated in FIG. 11, even when one segmented cutting edge 122constituting the cutting edge portion 120, for example, the finishingcutting edge 122 a was positioned at an accurate position with respectto the tooth groove, it was found that another segmented cutting edge122 constituting the cutting edge portion 120, for example, the secondcoarse cutting edge 122 cc (indicated by a two-dot broken line in FIG.11) was not positioned at an accurate position with respect to a toothgroove. As a result of investigating this phenomenon in detail, it wasfound that there was a variation in an amount of deviation of each ofthe coarse cutting edges 122 b and 122 c with respect to the toothgroove of the workpiece W depending on a distance d from a virtual planePw including the workpiece center axis Aw and a position at which thefinishing cutting edge 122 a was in contact with the workpiece W.Therefore, by changing the helix angles α1 and α2 of the coarse cuttingedges 122 b and 122 c with respect to the helix angle α0 of thefinishing cutting edge 122 a as described above, all the segmentedcutting edges 122 constituting the cutting edge portion 120 can bepositioned at accurate positions with respect to the tooth grooves ofthe workpiece W. As described above, when the helix angle α of the toothtrace L is changed in accordance with a position in the axial directionDa of the tooth trace L, positions of the plurality of segmented cuttingedges 122 in the circumferential direction Dc are different from a casein which the helix angle α is constant at each position in the axialdirection Da.

Since the helix angle α1 and α2 of each of the coarse cutting edges 122b and 122 c are changed with respect to the helix angle α0 of thefinishing cutting edge 122 a as described above, the skiving cutter 100of the present embodiment allows all the segmented cutting edges 122constituting the cutting edge portion 120 to be positioned at accuratepositions with respect to the tooth grooves of the workpiece W asdescribed above. Therefore, in the skiving cutter 100 of the presentembodiment, the processing accuracy for the workpiece W can be enhanced.In addition, in the skiving cutter 100 of the present embodiment, sinceall the segmented cutting edges 122 constituting the cutting edgeportion 120 can be positioned at accurate positions with respect totooth grooves of the workpiece W, a load applied to each of thesegmented cutting edges 122 constituting the cutting edge portion 120can be reduced and a service life of the skiving cutter 100 can beprolonged.

In the present embodiment, one cutting edge portion 120 has four or fivesegmented cutting edges 122, of which three of the segmented cuttingedges 122 contribute to the skiving processing. However, one cuttingedge portion 120 may have three segmented cutting edges 122, of whichtwo segmented cutting edges 122 may contribute to the skivingprocessing, or one cutting edge portion 120 may have five segmentedcutting edges 122 or more, of which four segmented cutting edges 122 ormore may contribute to the skiving processing.

Second Embodiment

A second embodiment of a skiving cutter will be described with referenceto FIG. 12.

As in the skiving cutter 100 of the first embodiment, a skiving cutter200 of the present embodiment includes a base 210 and a plurality ofcutting edge portions 220 protruding from an outer circumferentialsurface of the base 210. The base 210 of the present embodiment has ashape of a portion on the distal end side Daa of the barrel-shaped base110 in the first embodiment described above or a truncated cone shapewith the cutter center axis Ac as a center. Therefore, the base 210 hasa circular cross-sectional shape perpendicular to a cutter center axisAc at any position in an axial direction Da. In the base 210, an outerdiameter of an end on an attachment side Dab is the largest, and theouter diameter gradually decreases toward a distal end side Daa.

The plurality of cutting edge portions 220 are separated from each otherin a circumferential direction Dc. A tooth trace L of each of thecutting edge portions 220 extends in a direction inclined with respectto the cutter center axis Ac. Also, the cutting edge portion 220 isdivided into a plurality of segmented cutting edges 222 by cutting edgegrooves 221 extending in a direction intersecting the tooth trace L. Inthe present embodiment, an axis-cutting edge distance D0 of thesegmented cutting edge 222 furthest toward the attachment side Dab isthe largest among axis-cutting edge distances D of the plurality ofsegmented cutting edges 222 constituting the cutting edge portion 220,and the axis-cutting edge distance D gradually decreases toward thesegmented cutting edge 222 on the distal end side Daa. In other words,in the present embodiment, among the plurality of segmented cuttingedges 222 constituting the cutting edge portion 220, the segmentedcutting edge 222 positioned furthest toward the attachment side Dabforms a finishing cutting edge (reference cutting edge) 222 a, and theother segmented cutting edges 222 form coarse cutting edges 222 b to 222e.

As in the segmented cutting edges 122 of the first embodiment, each ofthe segmented cutting edges 222 includes an outer circumferentialcutting edge, a pair of side cutting edges, a cutting face, anperipheral relief face, a back face, and a pair of side flank faces. Arake angle of the cutting face, an peripheral relief angle of theperipheral relief face, a back face angle of the back face, and a siderelief angle of the side flank face are all within the angular rangesdescribed in the first embodiment. Dimensional relationships between therespective cutting edge heights of the plurality of segmented cuttingedges 222 constituting the cutting edge portion 220 are the same as therelationships described in the first embodiment. In addition,dimensional relationships between the respective cutting edge widths ofthe plurality of segmented cutting edges 222 constituting the cuttingedge portion 220 are the same as the relationships described in thefirst embodiment. Relationships between the respective helix angles ofthe plurality of segmented cutting edges 222 constituting the cuttingedge portion 220 are the same as the relationships described in thefirst embodiment.

As in the skiving cutter 100 of the first embodiment, also in theskiving cutter 200 of the present embodiment, since each of the coarsecutting edges 222 b to 222 e has a helix angle α which is different froma helix angle α of the finishing cutting edge 222 a, the processingaccuracy for a workpiece W can be enhanced and a service life of theskiving cutter 200 can be prolonged.

Further, as described above, since the segmented cutting edge 222positioned furthest toward the attachment side Dab forms the finishingcutting edge (reference cutting edge) 222 a, and the other segmentedcutting edges 222 form the coarse cutting edges 222 b to 222 e, theskiving cutter 200 of the present embodiment allows all the segmentedcutting edges 222 to contribute to the processing of the workpiece W.

In the present embodiment, one cutting edge portion 220 has four or fivesegmented cutting edges 222. However, the number of segmented cuttingedges 222 included in one cutting edge portion 220 may be less thanthis, and may be more than this.

Third Embodiment

A third embodiment of a skiving cutter will be described with referenceto FIGS. 13 to 15.

As illustrated in FIGS. 13 and 14, as in the skiving cutter 100 of thefirst embodiment, a skiving cutter 300 of the present embodimentincludes a base 310 and a plurality of cutting edge portions 320protruding from an outer circumferential surface of the base 310. Alsoin the base 310 of the present embodiment, a cross-sectional shapeperpendicular to a cutter center axis Ac is circular at any position inan axial direction Da.

As illustrated in FIG. 15, the base 310 of the present embodimentincludes a plurality of segmented bases 311 arranged in the axialdirection Da and separable from each other, and a positioning pin 319.The number of segmented bases 311 in the present embodiment is three.Among the plurality of segmented bases 311, an outer diameter of asegmented base 311 a furthest toward the attachment side Dab is thelargest, and the outer diameter decreases toward segmented bases 311 band 311 c on a distal end side Daa.

The plurality of cutting edge portions 320 are separated from each otherin a circumferential direction on the outer circumferential surface ofthe base 310. A tooth trace L of each of the cutting edge portions 320extends in a direction inclined with respect to the cutter center axisAc. Also, the cutting edge portion 320 is divided into a plurality ofsegmented cutting edges 322 by cutting edge grooves 321 extending in adirection intersecting the tooth trace L. In the present embodiment, thenumber of segmented cutting edges 322 constituting one cutting edgeportion 320 is three which is the same as the number of segmented bases311. Each of the segmented cutting edges 322 constituting one cuttingedge portion 320 is formed on a different segmented base 311. Therefore,among the plurality of segmented cutting edges 322 constituting each ofthe plurality of cutting edge portions 320, a segmented cutting edge rowwhich is a collection of a plurality of segmented cutting edges 322having the same position in the axial direction Da as each other andarranged in the circumferential direction is formed in one segmentedbase 311.

As illustrated in FIG. 15, an attachment hole 312 penetrating in theaxial direction Da is formed in each of the plurality of segmented bases311. Inner diameters of the attachment holes 312 of the plurality ofsegmented bases 311 are the same. A key groove 313 recessed from aninner circumferential surface of the attachment hole 312 to a radialouter side with respect to the cutter center axis Ac is further formedin the segmented base 311. The key groove 313 extends in the axialdirection Da from an end face on the attachment side Dab to an end faceon the distal end side Daa of the segmented base 311. A pin hole 318which is parallel to the cutter center axis Ac and penetrating in theaxial direction Da is further formed in the plurality of segmented bases311.

Among axis-cutting edge distances D of the plurality of segmentedcutting edges 322 constituting the cutting edge portion 320, anaxis-cutting edge distance D of the segmented cutting edge 322 furthesttoward the attachment side Dab, that is, the segmented cutting edge 322formed on the segmented base 311 furthest toward the attachment side Dabis the largest, and the axis-cutting edge distance D gradually decreasestoward the segmented cutting edge 322 on the distal end side Daa. Inother words, also in the present embodiment, as in the secondembodiment, among the plurality of segmented cutting edges 322constituting the cutting edge portion 320, a segmented cutting edge 322positioned furthest toward the attachment side Dab forms a finishingcutting edge (reference cutting edge) 322 a, and the other segmentedcutting edges 322 form coarse cutting edges 322 b and 322 c. Therefore,among the plurality of segmented bases 311, a plurality of finishingcutting edges 322 a are formed only on the segmented base 311 a furthesttoward the attachment side Dab. In the present embodiment, the segmentedbase 311 a and the plurality of finishing cutting edges 322 a constitutea finishing cutting edge cutter piece 301 a. Among the plurality ofsegmented bases 311, a plurality of first coarse cutting edges 322 b areformed only on a segmented base 311 b adjacent to the segmented base 311a on which the finishing cutting edges 322 a are formed. In the presentembodiment, the segmented base 311 b and the plurality of first coarsecutting edges 322 b constitute the first coarse cutting edge cutterpiece 301 b. A plurality of second coarse cutting edges 322 c are formedonly on a remaining segmented base 311 c among the plurality ofsegmented bases 311. In the present embodiment, the segmented base 311 cand a plurality of second coarse cutting edges 322 c constitute a secondcoarse cutting edge cutter piece 301 c.

As in the segmented cutting edges 122 of the first embodiment, each ofthe segmented cutting edges 322 includes an outer circumferentialcutting edge, a pair of side cutting edges, a cutting face, anperipheral relief face, a back face, and a pair of side flank faces. Arake angle of the cutting face, an peripheral relief angle of theperipheral relief face, a back face angle of the back face, and a siderelief angle of the side flank face are all within the angular rangesdescribed in the first embodiment. Dimensional relationships between therespective cutting edge heights of the plurality of segmented cuttingedges 322 constituting the cutting edge portion 320 are the same as therelationships described in the first embodiment. In addition,dimensional relationships between the respective cutting edge widths ofthe plurality of segmented cutting edges 322 constituting the cuttingedge portion 320 are the same as the relationships described in thefirst embodiment. Dimensional relationships between the respective helixangles α of the plurality of segmented cutting edges 322 constitutingthe cutting edge portion 320 are the same as the relationships describedin the first embodiment.

As described above, the base 310 of the present embodiment isconstituted to include the plurality of segmented bases 311 which areseparable from each other. Therefore, a positional relationship betweenthe plurality of segmented bases 311 can be changed in the axialdirection Da, and the positional relationship therebetween can bechanged also in the circumferential direction with respect to the cuttercenter axis Ac. In the present embodiment, it is extremely important toaccurately determine the positional relationship in the circumferentialdirection Dc between the plurality of segmented cutting edges 322constituting the cutting edge portion 320 of the skiving cutter 300.

When the skiving cutter 300 is attached to the cutter arbor 10, first,the cutter attachment portion 12 of the cutter arbor 10 is inserted intoeach of the attachment holes 312 of the plurality of segmented bases311. Next, mutual positional relationships in the circumferentialdirection between the plurality of segmented bases 311 are adjusted sothat the pin holes 318 of the plurality of segmented bases 311 arelinearly continuous. Then, the positioning pin 319 serving as apositioning member is inserted into each of the pin holes 318 of theplurality of segmented bases 311. As a result, in the presentembodiment, it is possible to accurately determine the mutual positionalrelationships in the circumferential direction between the plurality ofsegmented cutting edges 322 constituting the cutting edge portion 320.Thereafter, the key 17 is inserted into the key space formed by the keygrooves 313 of the plurality of segmented bases 311 and the key groove13 of the cutter arbor 10. Then, a fixing nut 18 is screwed into themale screw 14 of the cutter arbor 10. As a result, the plurality ofsegmented bases 311 are interposed between the held portion 15 of thecutter arbor 10 and the fixing nut 18, and thus the mutual positionalrelationships are determined in the axial direction Da and the pluralityof segmented bases 311 are fixed to the cutter arbor 10. Thereby,attachment of the skiving cutter 100 of the present embodiment to thecutter arbor 10 is completed.

As in the skiving cutter 100 of the first embodiment, also in theskiving cutter 300 of the present embodiment, since each of the coarsecutting edges 322 b and 322 c has a helix angle α different from a helixangle α of the finishing cutting edge 322 a, the processing accuracy fora workpiece W can be enhanced and a service life of the skiving cutter300 can be prolonged.

Also, as in the skiving cutter 200 of the second embodiment, since thesegmented cutting edge 322 positioned furthest toward the attachmentside Dab forms the finishing cutting edge (reference cutting edge) 322a, and the other segmented cutting edges 322 form the coarse cuttingedges 322 b and 322 c, the skiving cutter 300 of the present embodimentallows all the segmented cutting edges 322 to contribute to theprocessing of the workpiece W.

Further, the base 310 of the skiving cutter 300 of the presentembodiment is constituted by the segmented bases 311 that are separablefrom each other, and furthermore, among the plurality of segmentedcutting edges 322 constituting one cutting edge portion 320, only onesegmented cutting edge 322 is formed on one segmented base 311.Therefore, among the plurality of segmented cutting edges 322constituting one cutting edge portion 320, it is possible to process onesegmented cutting edge 322 without interfering with the other segmentedcutting edges 322 constituting the cutting edge portion 320. Therefore,in the present embodiment, the segmented cutting edge 322 can be easilyprocessed.

Fourth Embodiment

A fourth embodiment of a skiving cutter will be described with referenceto FIG. 16.

A skiving cutter 400 of the present embodiment is basically the same asthe skiving cutter 300 of the third embodiment. That is, the skivingcutter 400 of the present embodiment includes a finishing cutting edgecutter piece 401 a, a first coarse cutting edge cutter piece 401 b, asecond coarse cutting edge cutter piece 401 c, and a positioning pin419. Each of the cutter pieces 401 a, 401 b, and 401 c includes onesegmented base 411 and a plurality of segmented cutting edges 422. Thebase 410 is constituted by three segmented bases 411. One cutting edgeportion 420 is constituted by one segmented cutting edge 422 of thefinishing cutting edge cutter piece 401 a, one segmented cutting edge422 of the first coarse cutting edge cutter piece 401 b, and onesegmented cutting edge 422 of the second coarse cutting edge cutterpiece 401 c. Parameters of the plurality of segmented cutting edges 422constituting the cutting edge portion 420 are basically the same as theparameters of the segmented cutting edges in the above embodiments.However, a helix angle α of each of the segmented cutting edges 422 inthe present embodiment is 10° or less, and an outer circumferentialcutting edge 423 of each segmented cutting edge 422 is in a virtualplane Pb which is perpendicular to a cutter center axis Ac.

In each of the embodiments described above, the helix angle α of thesegmented cutting edge has been larger than 10°. In this case, the outercircumferential cutting edge of the segmented cutting edge is in thevirtual plane perpendicular to a tooth trace L. In the segmented cuttingedge of the skiving cutter, a direction in which the tooth trace Lextends is a cutting direction. Therefore, when the outercircumferential cutting edge is in the virtual plane perpendicular tothe tooth trace L, that is, when the outer circumferential cutting edgeextends in a direction perpendicular to the tooth trace L, cutting loadsat portions on both sides of the outer circumferential cutting edge aremade equal and an amount of wear at each position on the outercircumferential cutting edge can be made uniform.

The outer circumferential cutting edge 423 of the present embodiment isnot within the virtual plane perpendicular to the tooth trace L.However, in a case in which the helix angle α of the segmented cuttingedge 422 is 10° or less as in the present embodiment, although the outercircumferential cutting edge 423 is not within the virtual planeperpendicular to the cutter center axis Ac, this outer circumferentialcutting edge 423 is in the virtual plane substantially perpendicular tothe tooth trace L. Therefore, also in the present embodiment, cuttingloads at portions on both sides of the outer circumferential cuttingedge 423 are made substantially equal and an amount of wear at eachposition on the outer circumferential cutting edge 423 can be madesubstantially uniform. Further, in the present embodiment, the pluralityof segmented cutting edges 422 formed on each of the cutter pieces 401a, 401 b, and 401 c have the same position as each other in an axialdirection Da and the outer circumferential cutting edges 423 are in thevirtual plane Pb perpendicular to the cutter center axis Ac. Therefore,the outer circumferential cutting edges 423 of the plurality ofsegmented cutting edges 422 formed on each of the cutter pieces 401 a,401 b, and 401 c are in one virtual plane Pb perpendicular to the cuttercenter axis Ac. Therefore, in the present embodiment, each of the outercircumferential cutting edges 423 of the plurality of segmented cuttingedges 422 formed on each of the cutter pieces 401 a, 401 b, and 401 c,and a cutting face which is continuous with the outer circumferentialcutting edge 423 can be processed together with mutually adjacentsegmented cutting edges 422 in the circumferential direction.

In the present embodiment and the third embodiment, one cutting edgeportion includes three segmented cutting edges. In other words, in thepresent embodiment and the third embodiment, three cutter pieces areprovided. However, the number of cutter pieces may be two, or four ormore. Further, in the present embodiment and the third embodiment, aplurality of cutter pieces separable from each other are provided.However, in the present embodiment and the third embodiment, a pluralityof cutter pieces may be an integral body and may have the same aspectsas in the first embodiment and the second embodiment.

INDUSTRIAL APPLICABILITY

According to the skiving cutter of one aspect of the present invention,an internal gear can be precisely formed into a target shape and aservice life of the skiving cutter can be prolonged.

REFERENCE SIGNS LIST

-   -   1 bed    -   2 column    -   3 saddle    -   4 head    -   5 slider    -   6 main spindle unit    -   7 rotary table    -   10 cutter arbor    -   12 cutter attachment portion    -   13 key groove    -   14 male screw    -   15 held portion    -   17 key    -   18 fixing nut    -   100, 200, 300, 400 skiving cutter    -   301 a, 401 a finishing cutting edge cutter piece    -   301 b, 401 b first coarse cutting edge cutter piece    -   301 c, 401 c second coarse cutting edge cutter piece    -   110, 210, 310, 410 base    -   311, 411 segmented base    -   112, 312 attachment hole    -   113, 313 key groove    -   318 pin hole    -   120, 220, 320, 420 cutting edge portion    -   121, 221, 321 cutting edge groove    -   122, 222, 322, 422 segmented cutting edge    -   122 a, 222 a, 322 a finishing cutting edge    -   122 b, 322 b first coarse cutting edge    -   122 c, 322 c second coarse cutting edge    -   222 b, 222 c, 222 d, 222 e coarse cutting edge    -   123, 423 Outer circumferential cutting edge    -   124 Side cutting edge    -   125 cutting face    -   126 peripheral relief face    -   127 back face    -   128 side flank face    -   319, 419 positioning pin (positioning member)    -   L tooth trace    -   W workpiece    -   Lw tooth trace    -   Aa arbor center axis    -   Ac cutter center axis    -   Ah head center axis

1. A skiving cutter comprising: a base having a circular cross-sectionalshape perpendicular to an axis; and a plurality of cutting edge portionsprotruding from an outer circumferential surface of the base, formed atintervals in a circumferential direction with respect to the axis, andhaving a tooth trace extending in a direction inclined with respect tothe axis, wherein each of the cutting edge portions is segmented into aplurality of segmented cutting edges by cutting edge grooves extendingin a direction intersecting the tooth trace, each of the segmentedcutting edges includes an outer circumferential cutting edge which is anedge farthest away from the base among portions forming the segmentedcutting edge, and a helix angle which is an angle of the tooth tracewith respect to the axis is different according to a position in theaxial direction of the plurality of segmented cutting edges constitutingthe cutting edge portion.
 2. The skiving cutter according to claim 1,wherein the outer circumferential cutting edge of the segmented cuttingedge having a helix angle of 10° or less is in a virtual planeperpendicular to the axis.
 3. The skiving cutter according to claim 1,wherein the outer circumferential cutting edge of the segmented cuttingedge having the helix angle α larger than 10° is in a virtual planeperpendicular to the tooth trace.
 4. The skiving cutter according toclaim 1, comprising a plurality of cutter pieces arranged in the axialdirection, wherein each of the cutter pieces includes: a segmentedcutting edge row which is a collection of a plurality of segmentedcutting edges having the same position in the axial direction as eachother and arranged in the circumferential direction among the segmentedcutting edges constituting each of the plurality of cutting edgeportions; and a segmented base formed as a portion of the base andincluding the segmented cutting edge row formed on an outercircumference thereof, and the segmented bases are separable from eachother, and the skiving cutter further comprising: a positioning memberwhich determines relative positions in the circumferential direction ofthe segmented cutting edges between the plurality of cutter pieces.